Microsomal cytochromes P-450 play key roles in steroid biosynthesis in testis and adrenal gland and xenobiotic metabolism in liver. We propose to perform structure-function studies on the 17-Alpha-hydroxylase/C17, 20-lyase enzyme involved in androgen biosynthesis in testis and on the 17-Alpha-hydroxylase and 21-hydroxylase enzymes from adrenal gland. All three enzymes will be studied in pig as a model system. Structural studies will utilize the microsequencing methodology developed in our laboratory to obtain partial amino acid sequences and molecular cloning technology to obtain cDNA sequences. cDNA sequences will be used to align and complete amino acid sequences. cDNA sequences will be used to align and complete amino acid sequences. Specific active site modification by bromoacetoxysteroid derivaties will be used on all three enzymes. The kinetics of inactivation will be performed by Dr. Peter Hall at the Worcester Foundation (Shrewsbury, Mass.), and the sequencing of modified peptides by us. Since very little is known about the structures of microsomal cytochromes P-450, this work should provide a basis for the comparison of a number of these key enzymes.